Cynicism is an ancient Greek ethical doctrine which holds that the purpose of life is to live a life of Virtue in agreement with Nature (which calls for only the bare necessities required for existence). This means rejecting all conventional desires for health, wealth, power and fame, and living a life free from all possessions and property. However, rather than retreating from society, Cynics should live in the full glare of the public's gaze and would be quite indifferent in the face of any insults which might result from their unconventional behaviour. Their way of life requires continuous training (of both the mind and the body), not just an abdication of responsibility and a nihistic lifestyle.

The Cynics believed that the world belongs equally to everyone, and that suffering is caused by false judgments of what is valuable, and by the worthless customs and conventions which surround society. They also saw their job as acting as the watchdog of humanity, and to evangelize and hound people about the error of their ways. They were particularly critical of any show of greed, which they viewed as a major cause of suffering. Many of their ideas were later absorbed into Stoicism.

Although there was never an official Cynic doctrine, the fundamental principles can be summarised as:

The goal of life is happiness, which is to live in agreement with Nature.

Happiness depends on being self-sufficient, and a master of mental attitude.

Self-sufficiency is achieved by living a life of Virtue.

The road to Virtue is to free oneself from any influences (e.g. wealth, fame, power, etc) which have no value in Nature.

Suffering is caused by false judgments of value, which cause negative emotions and a vicious character.

The term "cynic" derives from the Greek "kunikos" (meaning "dog-like"), possibly as a pejorative reference to the first Cynics' shameless rejection of conventional manners and their decision to live on the streets. In common usage, "cynicism" means a disposition to disbelieve in the sincerity or goodness of human motives and actions, and a tendency to express this by sneers and sarcasm.

The real founder of Cynicism was Antisthenes (c. 445 - 365 B.C.), who had been one of the most important pupils of Socrates in the early 5th Century B.C. He preached a life of poverty, but his teachings also covered language, dialogue and literature in addition to the pure Ethics which the later Cynics focused on.

Antisthenes was followed by Diogenes of Sinope (who lived in a tub on the streets of Athens, and ate raw meat, taking Cynicism to its logical extremes), and by Crates of Thebes (c. 365 - 285 B.C.), who gave away a large fortune so he could live a life of Cynic poverty in Athens. Diogenes dominates the story of Cynicism like no other figure, and he came to be seen as the archetypal Cynic philosopher. He adopted a lifestyle of self-sufficiency ("autarkeia"), austerity ("askesis") and shamelessness ("anaideia"), and was famed for his biting satire and wit.

With the rise of Stoicism in the 3rd Century B.C., Cynicism as a serious philosophical activity underwent a decline, and it was not until the Roman era that there was a Cynic revival. Cynicism spread with the rise of Imperial Rome in the 1st Century A.D., and Cynics could be found begging and preaching throughout the cities of the Roman Empire, where they were treated with a mixture of scorn and respect. Cynicism seems to have thrived into the 4th Century A.D., unlike Stoicism, which had long declined by that time.

Cynicism finally disappeared in the late 5th Century A.D., although many of its ascetic ideas and rhetorical methods were adopted by early Christians.